COMPRESSOR BLADE

A blade (2) for a compressor comprising a pressure surface (6) and a suction surface (4), wherein the suction surface (4) comprises: a discontinuity in the chord-wise curvature of an intermediate portion of the suction surface between the blade leading edge and blade trailing edge; and a slot (20) arranged along at least a portion of the blade (2) in a substantially span-wise direction, the slot (2) being disposed at or near the said change in curvature, such that when in use lower momentum fluid near the suction surface (4) is aspirated into the slot (20).

Deformation and fracture of impulsively loaded sandwich panels

Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson-Cook constitutive relation and a Cockcroft-Latham fracture criterion that accounted for local variation in material properties. The fully coupled simulation approach enabled the relationships between the soil-explosive test charge design, panel geometry, spatially varying material properties and the panel's deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel's surface topology. Significant fluid-structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system. © 2012 Elsevier Ltd. All rights reserved.

Finite Element studies on indentation size effect using a higher order strain gradient theory

In this work, a Finite Element implementation of a higher order strain gradient theory (due to Fleck and Hutchinson, 2001) has been used within the framework of large deformation elasto-viscoplasticity to study the indentation of metals with indenters of various geometries. Of particular interest is the indentation size effect (ISE) commonly observed in experiments where the hardness of a range of materials is found to be significantly higher at small depths of indentation but reduce to a lower, constant value at larger depths. That the ISE can be explained by strain gradient plasticity is well known but this work aims to qualitatively compare a gamut of experimental observations on this effect with predictions from a higher order strain gradient theory. Results indicate that many of the experimental observations are qualitatively borne out by our simulations. However, areas exist where conflicting experimental results make assessment of numerical predictions difficult. © 2012 Elsevier Ltd. All rights reserved.

Polyphasic characterization of water bloom forming Raphidiopsis species (cyanobacteria) from central China

Two strains of Raphidiopsis Fritsch et Rich were isolated from a fishpond in Wuhan city, China and rendered axenic, and characterized by a combination of morphological, physiological, biochemical and genetic methods. Morphologically the strains were identified as Raphidiopsis mediterranea Skuja (straight trichomes) and R. curvata Fritsch et Rich (coiled trichomes). These two strains demonstrated slight differences in optimal temperature range and GC content, while sharing some common characteristics including inability to grow hetertrophically, similar salinity tolerance (up to 0.78%) and an identical fatty acid composition. Cyanotoxins were not found in the strain of R. mediterranea, however, the strain of R. curvata contained both deoxycylindrospermopsin and cylindrospermopsin. Phylogenetic affiliations inferred from 16S rRNA gene sequences demonstrated that both Raphidiopsis strains clustered with Cylindrospermopsis, demonstrating their phylogenetic ties to Nostocaceae. (c) 2007 Elsevier B.V. All rights reserved.

LIPID MICRORESISTOR AS MIMICKING OLFACTORY SENSOR - THE RULE OF THE RESPONSE OF LIPIDS TO C-1-C-4 ALCOHOLS

Phosphatidylcholine (PC) and six other PC-similar lipids are coated on interdigital electrodes, IEs, as sensitive membranes. Eight alcohols (C-1-C-4) are tested in a flow system at room temperature. It is found that all responses are log(response)-log(concentration) linear relations. These results agree with Steven's law in psychophysics. Moreover, the thresholds of the sensors are coincident with human olfactory thresholds. The authors have analysed the data of the lipid hypothesis suggested by Kurihara et al. We have found that this hypothesis is also in agreement with Steven's law. Lipid microresistors are real mimicking olfactory sensors. A definition of an olfactory sensor is suggested.

First principles based predictions of the toughness of a metal/oxide interface

We describe a first-principles-based strategy to predict the macroscopic toughness of a gamma-Ni(Al)/alpha-Al2O3 interface. Density functional theory calculations are used to ascertain energy changes upon displacing the two materials adjacent to the interface, with relaxation conducted over all atoms located within adjoining rows. Traction/displacernent curves are obtained from derivatives of the energy. Calculations are performed in mode I (opening), mode II (shear) and at a phase angle of 45 degrees. The shear calculations are conducted for displacements along < 110 > and < 112 > of the Ni lattice. A generalized interface potential function is used to characterize the results. Initial fitting to both the shear and normal stress results is required to calibrate the unknowns. Thereafter, consistency is established by using the potential to predict other traction quantities. The potential is incorporated as a traction/displacement function within a cohesive zone model and used to predict the steady-state toughness of the interface. For this purpose, the plasticity of the Ni alloy must be known, including the plasticity length scale. Measurements obtained for a gamma-Ni superalloy are used and the toughness predicted over the full range of mode mixity. Additional results for a range of alloys are used to demonstrate the influences of yield strength and length scale.

薄膜/基体界面的层裂行为研究

近年来，薄膜/基体结构在微/纳米工程中得到广泛的应用，研究薄膜/基体界面的力学性能得到广泛的关注。为了检验薄膜和基体间的黏结强度，早在20世纪50年代，人们就设计了一种简单的实验方法－－撕裂试验，该试验由于其简单易于操作至今仍在许多领域都有广泛的应用。早期对于撕裂试验的研究多局限于弹性撕裂，即将薄膜和基体都作为弹性材料来处理。后来，对于韧性薄膜，为了预测由于塑性耗散引起能量释放率(撕裂力)的增大，Kim及其合作者提出并采用了梁的弯曲模型对撕裂中的塑性耗散进行预测。Wei和Hutchinson在分析弹塑性薄膜的撕裂问题时，采用了一种不同于Kim的弯曲模型的方法，除已脱胶部分之外，薄膜的脱胶过程由平面应变弹塑性有限元方法模拟，在分析过程中采用黏聚力模型来刻画韧性薄膜沿基体界面被撕裂或脱胶过程，所得结果无论是在定性还是定量上均与Kim的梁弯曲模型结果有很大区别。\newline 鉴于几种关于韧性薄膜撕裂模型对结果预测的不一致，几位学者联名倡议提出开展关于薄膜撕裂实验刻画模型有效性检验的国际合作。在倡议中指出无论采用何种方法，都须采用黏聚力模型来刻画界面断裂过程。而此后有很多工作都采用黏聚力模型来刻画界面。\newline 如果考虑残余应力的影响，涂层或黏结于基体上的薄膜或多层材料中的单独片层等均不可避免地承受着残余应力的作用。薄膜中的残余应力的主要来源于沉积过程，外延，以及热膨胀失配等因素。承受应力状态的薄膜/基体体系往往在边缘处产生很强的应力集中，极易导致其在该处界面起始层裂发生。如何评价残余应力对薄膜/基体体系界面的影响也显得至关重要。\newline 本文将对撕裂试验以及热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为展开研究。薄膜/基体体系界面采用混合性黏聚力模型来刻画。研究了对应不同薄膜材料参数和不同界面参数情况下的撕裂行为，给出了撕裂力和界面分离功以及界面分离强度等参数之间的关系，并对界面层裂模式进行了分析。同时对多角度撕裂的界面破坏形式进行了系统的研究，给出了稳态撕裂力及相角与撕裂角度之间的关系。\newline 对由于热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为的研究。假设薄膜和基体材料分别为弹塑性材料和弹性材料。研究了对应不同薄膜材料参数和不同界面参数情况的界面层裂发生机制，给出了层裂发生时临界温度荷载与薄膜/基体几何参数、材料参数以及模型参数之间的关系。